This invention relates generally to camshafts for machines and more particularly to lightweight assembled camshafts for motor vehicle engines and methods for assembling such camshafts.
Assembled camshafts for motor vehicles and other machines have been made for more than 60 years, in order to decrease cost and weight of the camshafts relative to those made by conventional casting, forging, machining, grinding, hardening and straightening techniques. In some cases, the camshafts have been built up from several segments which were assembled and welded end-to end to form the shaft. In other cases, the cam and journal elements have been preformed with cylindrical axial bores, by casting, forging, or powder metallurgy techniques, and positioned on a shaft or hollow tube and welded in place. In still other cases, preformed elements having axially extending radial depressions have been positioned on a hollow tube and the tube has been expanded, usually by forcing a tool with one or more radial projections through the tube, to lock the cam and journal elements in desired radial and axial positions thereon.
Additional weight reduction has been attained, as taught in U.S. Pat. 5,201,246, to Arnold, et al., by forming cam and journal elements, preferably from sheet metal, with outer walls and hubs connected by webs at one axial end of the walls and hubs and attaching those elements to a hollow tube by expanding the tube within the hubs. One important limitation of this technique is the fact that the minimum base circle of the cam and journal elements which can practically be made by this technique is more than the diameter of the tube plus at least six times the thickness of the material from which the elements are made. This limitation is due to the minimum thickness of the forming tool necessary for making a "U"-bend in the material between the hub and outer wall to form the element and, thus, excludes elements with small base circles from application of fabrication by this technique.
Thus, virtually all cam and journal elements for assembled camshafts are currently made by casting, forging, or powder metallurgy techniques; thereby failing to achieve their full potential savings of cost and weight. Moreover, the assembly techniques possible for assembling the cam and journal elements on a tubular shaft have been necessarily limited by the design of the elements to those which rely on expansion of the tubular member to lock the elements in their required axial and radial orientations. This has resulted in increased heat treatment and straightening costs as well as increased capital costs for precision assembly equipment.
The foregoing illustrates limitations known to exist in present assembled camshafts. Thus, it would clearly be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.